1. Field of the Invention
This invention relates to domain transport stores, and in particular to a method and apparatus for creating a high frequency rotating magnetic field for causing movement of cylindrical domains along paths prescribed by the manipulation pattern of the store.
2. Description of the Prior Art
Domain transport stores have a block, in particular layerlike storage medium, consisting of magnetic garnet or orthoferrite for example and having magnetized cylindrical domains which extend perpendicular to the layer plane, whereby the magnetization is opposite to the magnetization of the surrounding area and to a magnetic supporting field serving for the stabilization of the cylindrical domains, and aligned perpendicular to the plane of the layer and a preferably periodic manipulation pattern. The individual elements of the magnetizable material, in particular consisting of a magnetostriction-free NiFe alloy are applied in layers, or in a rectangular manner, onto one of the layer surfaces. For the manipulation of the cylinder domains a high frequency rotary magnetic field is utilized, which field has a field vector which rotates parallel to the plane of the layer.
In the above-mentioned magnetic rotary field, the individual elements of the manipulation pattern create magnetic scatter fields under whose effect cylindrical domains travel to energetically more favorable positions at the individual elements. In case of a suitable geometry of the manipulation pattern, the cylindrical domains move in a complete rotation of the rotary magnetic field by one period of the manipulation pattern, which means that they are stepped along one storage location at a time. In a continuously rotating magnetic field, therefore, the cylindrical domains can be transported along paths prescribed by the manipulation pattern.
The rotary magnetic field required for transport of the cylindrical domains, as is generally known, is created in a pair of coils, commonly known as Helmholtz coils, which are perpendicularly oriented in respect of each other, whereby, for energy considerations, the individual coils are in each case supplemented by capacitances to form resonant circuits which are controlled by a sine or cosine current, respectively. In order to receive an ideally rotating magnetic field in the operating space of the pair of coils, the phase position and the amplitude of the control currents must be observed, since only with equal amplitudes and correct phasing is it guaranteed that a circle is prescribed by the terminal point of the rotating magnetic field vector.